1. Field of the Invention
The present invention relates to fluid pump apparatus and more specifically to those for use for example for artificial hearts, employing a magnetic bearing to magnetically levitate an impeller to deliver fluid such as blood.
2. Description of the Background Art
FIG. 15 is a vertical cross section of one example of a body of a blood pump as one example of a conventional fluid pump apparatus. In FIG. 15, the pump body includes a cylindrical housing 1 internally partitioned axially by partitions 11, 12, 13 and 14 to accommodate an electromagnet unit 20, a pump unit 30 and a motor unit 40. Electromagnet unit 20 has an electromagnet 21 and a magnetic bearing sensor 22 incorporated therein. Casing 1 has on the electromagnet unit 20 side (or one side) a side wall having a center provided with an inlet 15 introducing blood. At least three electromagnets 21 and at least three magnetic bearing sensors 22 surround inlet 15 circumferentially. Electromagnets 21 and magnetic bearing sensors 22 are attached to an internal wall surface of partition 11 externally isolating electromagnet unit 20.
In pump unit 30 an impeller 31 is rotatably housed and it has a portion closer to electromagnet unit 20 that is supported by electromagnet unit 21 contactless through partition 12, and magnetic bearing sensor 22 senses the distance between magnetic bearing sensor 22 and one side of impeller 31. Impeller 31 has the other side with a plurality of permanent magnets 32 buried therein circumferentially.
Motor unit 40 houses a motor stator 41 and motor rotor 42. Motor stator 41 is arranged on an external peripheral surface of a cylindrical member 43 extending cylindrically from an internal wall surface of partition 14 externally partitioning motor unit 40. Motor rotor 42 rotates around a shaft supported by an internal peripheral surface of cylindrical member 43 via a motor bearing 44 provided in the form of a ball or roller bearing. Motor rotor 42 has an inner peripheral surface provided with a permanent magnet 47 facing an electromagnet 46 of motor stator 41 and motor rotor 42 rotates through their magnetic force, borne by motor bearing 44. Motor rotor 42 has a surface facing pump unit 30 and having a plurality of permanent magnets 45 buried therein circumferentially, opposite to permanent magnet 32 buried in impeller 31, through partition 13.
In the blood pump apparatus thus configured, magnetic bearing sensor 22 provides an output which is referred to by a controller 10, described hereinafter, to control a current flowing to electromagnet 21, to control an attractive force provided by electromagnet 21 toward the opposite side of impeller 31.
Furthermore impeller 31 has a portion closer to motor unit 40 that is affected by the attractive force introduced by permanent magnets 32 and 45. And impeller 31 is magnetically levitated by a non-controlled bearing provided by permanent magnets 32 and 45 and a controlled bearing provided by electromagnet 21. Impeller 31 is rotated by a driving force of motor unit 40 and blood introduced through inlet 15 is output through an outlet (not shown) formed at pump unit 30.
In the FIG. 15 fluid pump apparatus, electromagnet 21 generates heat attributed to a current flowing to magnetically levitate impeller 31 and motor stator 41 generates heat attributed to a current flowing to rotate motor rotor 42. Furthermore, motor bearing 44 is provided for example in the form of a ball or roller bearing and generates heat through friction as motor rotor 42 rotates. Furthermore, to externally release the heat generated by electromagnet 21, electromagnet 21 and magnetic bearing sensor 22 are fixed on an internal wall surface of partition 11 provided in contact with an outside of casing 1, and motor stator 41 is also provided at an internal wall surface of partition 14 provided in contact with an outside of casing 1, at an external peripheral surface of cylindrical member 43. Thus casing 1 is increased in temperature by the heat generated by electromagnet 21 and motor stator 41.
When the heat increases temperature, the heat is transferred to magnetic bearing sensor 22 and the sensor consequently has a temperature drift, which disadvantageously results in unreliable sensing.
Furthermore if fluid pump apparatus in FIG. 15 is used for example as a blood pump and thus configures a portion of an artificial heart and implanted in a human body the heat generated as described above may have a negatively effect on the tissues of the human body. This needs to be addressed by an approach taken separately. Such approaches to be taken, however, would increase the blood pump in size. Thus it is impossible to reduce the blood pump for the artificial heart in size or weight.
FIG. 16 is a block diagram showing a controller driving the conventional fluid pump apparatus shown in FIG. 15.
In FIG. 16, controller 10 includes a sequence circuit 101 externally receiving a control signal corresponding to commands for rotation, levitation and the like, an AC-DC converter 102 receiving an AC power supply, and a monitor circuit 103 monitoring the blood pump""s operation and externally communicating the condition. AC-DC converter 102 converts an AC voltage to a DC voltage which is in turn applied to a motor power amplifier 104, a magnetic bearing power amplifier 124 and a DC-DC converter 105. DC-DC converter 105 stabilizes the DC voltage and supplies it to a circuit as described hereinafter.
Controller 10 also includes a sensor circuit 110 having a carrier wave generation circuit 111, a tuning circuit 112 and an amplifier 113 incorporated therein. Carrier wave generation circuit 111 generates a carrier wave which is in turn provided via a connector 150 to magnetic bearing sensor 22 housed in housing 1 of the pump body. Magnetic bearing sensor 22, as shown in FIG. 15, outputs a signal having an amplitude corresponding to a distance between magnetic bearing sensor 22 and impeller 31. Tuning circuit 112 is tuned in to the signal to extract a detection signal, amplifier 113 amplifies the detection signal and provides it to magnetic bearing control circuit 121.
A magnetic bearing control circuit 121 receives the detection signal, responsively provides PID control, and feeds the control output to a magnetic bearing PWM circuit 122. Magnetic bearing PWM circuit 122 uses pulse width modulation (PWM) to vary the received control signal in pulse width. A magnetic bearing gate drive circuit 123 is operative to control a magnetic bearing power amplifier 124 to drive electromagnet 21.
Furthermore, a motor control circuit 131 outputs to a motor PWM circuit 132 a control signal based on a command input to sequence circuit 101. Motor PWM circuit 132 outputs a PWMed control signal to a motor gate drive circuit 133. Motor gate drive circuit 133 outputs a drive signal to motor power amplifier 104. In response to the drive signal, motor power amplifier 104 drives motor stator 41.
In the blood pump apparatus shown in FIGS. 15 and 16, magnetic bearing sensor 22 has characteristics slightly varying to reflect a difference of an individual blood pump from another individual one. As such, in sensor circuit 110 an adjustment needs to be made for each sensor. As such, controller 10 is not compatible with each blood pump, which is a bottleneck in mass production.
Furthermore, magnetic bearing power amplifier 124, motor power amplifier 104 and the like generate significant heat attributed to switching-loss and controller 10 would also generate heat, which can have a negative effect on a human body when the apparatus is implanted therein.
Therefore a main object of the present invention is to provide a fluid pump apparatus reduced in size and weight and capable of efficiently release heat.
Another object of the present invention is to provide a fluid pump apparatus capable of providing compatibility between the pump body and the controller and also using blood to cool a heated portion thereof.
The present invention provides a fluid pump apparatus including: a pump unit having in a casing a rotative member rotated to output a fluid; a drive unit coupled with one side of the rotative member contactless through a magnetic force to levitate one side of the rotative member while rotatably driving one side of the rotative member; a position detection unit detecting a position of the rotative member in levitation; and a controlled magnetic bearing unit contactlessly supporting the other side of the rotative member in response to an output of the position detection unit, wherein heat generated at least one of the rotative member, the position detection unit and the controlled magnetic bearing unit is released via a fluid flowing through the pump unit.
Thus in accordance with the present invention if a position detection unit receiving a sensor output to determine the position of the impeller in levitation is housed in the casing the position detection unit can have characteristics adjusted to correspond to the sensor of the body of the fluid pump to maintain compatibility with a controller.
Furthermore, if any of a drive circuit controlling the drive unit or a magnetic bearing control circuit controlling the controlled magnetic bearing unit is housed in the casing then heat generated from the drive circuit can be efficiently cooled by a fluid to prevent the controller body from generating significant heat.
Preferably, the casing includes a first partition provided between the pump unit and the drive unit and a second partition provided between the pump unit and the controlled magnetic bearing unit, and the drive unit is attached to the first partition and the controlled magnetic bearing unit is attached to the second partition.
More preferably the position detection unit is attached to the second partition.
Still more preferably, the rotative member is formed in a disk having a side facing the drive unit and provided with a permanent magnet arranged circumferentially and the rotative member and the drive unit are coupled contactless through magnetic-coupling.
Still more preferably, the rotative member is formed in a disk having a side facing the drive unit and provided with a first permanent magnet arranged circumferentially, the drive unit is provided with a second permanent magnet arranged circumferentially to face the first permanent magnet, and the first and second permanent magnets provide magnetic-coupling to couple the rotative member and the drive unit together contactlessly.
Still more preferably the controlled magnetic bearing unit includes a plurality of electromagnets each configured of a magnetic pole, a yoke and a coil and having an S magnetic pole and an N magnetic pole with at least the yoke and coil arranged circumferentially.
Still more preferably the drive unit includes a motor stator and a motor rotor rotated by a magnetic force of the motor stator, the motor stator being attached to the second partition.
Still more preferably the pump unit has an internal surface coated with an antithrombotic substance such as heparin.
The present invention in another aspect provides a fluid pump having a casing, an impeller driven, levitated, a drive unit driving the impeller, a sensor sensing a position of the impeller in levitation, and a controlled magnetic bearing unit contactlessly supporting the impeller in response to an output of the sensor, wherein the casing has housed therein at least one of the following circuits. The position detection circuit operative in response to the output of the sensor to determine the position of the impeller in levitation, the drive circuit controlling the drive unit, and the magnetic bearing control circuit controlling the controlled magnetic bearing.
If the position detection circuit is housed in the casing the position detection circuit can be adjusted to correspond to characteristics of the incorporated sensor and thus maintain compatibility with a controller. If the drive circuit or the magnetic bearing control circuit is housed in the casing, heat generated from the circuits can be cooled with a fluid flowing into the pump.
Preferably the fluid pump further includes an alternating current to direct current conversion circuit converting an alternating-current voltage to a direct-current voltage, and a direct current to direct current conversion circuit converting the converted direct-current voltage to a different direct-current voltage, wherein the direct current to direct current conversion circuit is housed in the casing. In this example also heat generated at the direct current to direct current conversion circuit can be cooled by a fluid.
More preferably the fluid pump apparatus further includes: a carrier wave generation circuit generating a carrier wave; and a tuning circuit detecting a signal of the sensor tuned in to the carrier wave generated by the carrier wave generation circuit, to detect the position of the impeller in levitation, wherein the carrier wave generation circuit and the tuning circuit are housed in the casing. As such, by adjusting the carrier wave generation circuit and the tuning circuit to correspond to the sensor""s characteristics, compatibility with a controller can be achieved.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.